Transgender youth, who identify with a gender that is different from their sex assigned at birth, are at increased risk for negative health outcomes due in part to stigmatization and family rejection. Research with non- transgender sexual minorities suggests that family support is crucial to youths' health and well-being and that family rejection may lead to negative outcomes, such as youth homelessness. Yet little is known about transgender youth specifically and how their experiences are linked to their current or past family environment (family of origin, chosen family, foster family, group care). In families with transgender youth, development of a transgender identity and the process of transitioning from assigned sex to identified gender may represent a source of stress for both the youth and the larger family system. Responding to the Institute of Medicine's and NIH LGBT Research Coordinating Committee's call for research on transgender-specific health needs, the specific aims of this research are to: 1) longitudinally investigate how the family environment affects health outcomes among transgender youth, 2) examine whether and what types of social support from within and outside of the family can improve family functioning and be protective for transgender youths' health, and 3) develop a narrative-based intervention to improve family functioning and social support-seeking behaviors in families with transgender youth. The Minority Stress Model and Family Systems Theory are integrated to provide a framework for Studies 1 and 2. Study 1 will investigate how the family environment is longitudinally associated with health outcomes (substance use, sexual risk, self-harm, suicidality, depression, anxiety) among transgender youth. With the goal of informing future interventions, Study 1 will also examine whether and what types of social support from within and outside of the family can improve family functioning and be protective for transgender youth's health. I will use community-based participatory research (CBPR) principles with mixed methods (qualitative interviews and quantitative surveys) to examine multiple aspects of the family environment, perceived stress, health outcomes, and social support using data collected at five waves across 24 months from 40 transgender youth ages 13 to 17 years and their parents/guardians and siblings (Total N = 80-160). Participants will be recruited from multiple sources to capture a diverse range of experiences and variability in family functioning. Previous research has indicated that social support may reduce negative stress-related outcomes in families with transgender youth. Interventions emphasizing social support are needed to ameliorate the effects of stressors and improve the family environment in this marginalized population. Study 2 will develop and pilot an innovative narrative-based intervention based on Social Cognitive and Transportation Theories to improve the family environment for transgender youth, including decreasing enacted stigma (overt anti-transgender attitudes and behaviors) within the family, and improving family functioning and social support-seeking skills. Narrative-based interventions use storytelling to promote health behavior change through mechanisms of transportation (absorption into the story and identification with characters), persuasion, and self-efficacy. The intervention developed in Study 2 will use digital storytelling, a specific narrative-based intervention method, to produce multimedia visual narratives from transgender youth about their family environment. Narrative-based interventions have been used successfully to change health behaviors and reduce stigma in marginalized populations, making this an innovative and promising approach to improve the family environment in families with transgender youth. The planned research will, for the first time, longitudinally investigate effects of the family environment on health outcomes among transgender youth using multiple family member perspectives and develop and pilot test a narrative-based intervention to improve the family environment for transgender youth. Ultimately this work will improve the health and well-being of transgender youth and families and inform future work with other marginalized populations.